1. Field of the Invention
The invention relates to a control apparatus and a control method for an internal combustion engine. More specifically, the invention relates to a control apparatus and a control method for an internal combustion engine that includes a variable valve operating mechanism and an EGR system.
2. Description of the Related Art
Japanese Patent Application Publication No. 2002-89341 (JP-A-2002-89341) describes a control apparatus that integrally controls a variable valve operating mechanism and Exhaust Gas Recirculation (EGR). The control apparatus includes a duration change mechanism that increases or decreases a lift and a duration of an intake valve; and a phase change mechanism that advances or retards a phase of a center angle of the lift. The lift, the duration, the phase of the center angle of the lift, and the amount of exhaust gas returned to an intake system for an internal combustion engine (i.e., the amount of EGR gas) are integrally controlled by controlling the mechanisms, according to a rate of change in a load of the internal combustion engine. Thus, the control apparatus increases fuel efficiency by reducing pump loss, and reduces the amount of NOx when the internal combustion engine is in any operating state.
In the internal combustion engine that includes the EGR system, when the operating state of the vehicle is changed to a low load operating state, the amount of the EGR gas is increased to reduce the amount of discharged NOx. When a demand for increasing the amount of the EGR gas is made, values of various control parameters are controlled to appropriate values corresponding to a target amount of the EGR gas. More specifically, in the internal combustion engine that includes the variable valve operating mechanism, in order to increase the amount of internal EGR gas, an opening timing of an intake valve is advanced by a predetermined amount to increase a valve overlap period in which the intake valve and an exhaust valve are open. Also, in order to increase an actual compression ratio to a target value, a closing timing of the intake valve is advanced by a predetermined amount.
In the variable valve operating mechanism that changes the phase and the duration of the intake valve separately, it is possible to set an execution timing of the phase control, and an execution timing of the duration control, separately. Therefore, it is preferable to set valve timings to minimize the amount of discharged NOx. Particularly, when the response of the duration change mechanism to the control is different from the response of the phase change mechanism to the control, for example, when the response of the duration change mechanism to the control is faster than the response of the phase change mechanism to the control, it is necessary to take into account the responses. However, in the above-described system, the execution timings of the controls are not accurately controlled. Thus, the above-described system needs to be improved.